Alkaline battery cathode structures incorporating multiple carbon materials and orientations

ABSTRACT

Cathode active materials for alkaline cells are disclosed. In particular, the cathode structures encompass conductive carbons introduced to the cathode so as to have a specific spatial orientation and/or a multi-carbon structure. The overall intent is to leverage the conductor(s) provided to the cathode structure to improve electronic and ionic conductance and, by extension, improve battery discharge performance.

FIELD OF INVENTION

The present invention relates to cathode active materials for alkalinecells. In particular, the present invention relates to cathodestructures incorporating conductive carbons possessing a specificspatial orientation and/or multi-carbon structure intended to improveelectronic and ionic conductance within the cathode itself.

BACKGROUND

The use of carbon materials as conductive aids in battery electrodes iswell-known. Virtually all battery systems using particulate materialscan be mixed with carbon-based particulates and/or coatings to improvethe conductivity and, by extension, discharge performance of theelectrode in which they are mixed. Despite the fact that many batterysystems rely on carbon conductors, the nature and use of theseconductors varies considerably depending upon the intended use anddischarge regime (e.g., anode vs. cathode; primary vs. secondary) andbattery chemistry (e.g., lithium-ion, lithium-iron disulfide, zinc-air,zinc-manganese dioxide, etc.).

For example, secondary batteries often rely on carbon electrodestructures to facilitate the ionic transport within the carbon materialduring charge and discharge cycling. Consequently, the combination ofspecific sources of carbons, as well as their orientation and structure,are dictated by the exigencies of this intended use. U.S. Pat. No.8,765,302 describes a graphene-enabled vanadium oxide compositecomposition for use as a lithium cathode (i.e., positive electrode)active material exhibiting unprecedented specific capacity, capacityretention and rate capability characteristics. U.S. Pat. No. 8,691,441discloses mutually bonded or agglomerated graphene sheets and particlesfor use in lithium battery cathode active materials.

Carbon structures for anode (i.e., negative electrode) materials insecondary cells are known and specifically optimized for ionicintercalation. U.S. Pat. No. 8,440,352 claims a fine carbon powderagglomerated onto the surface of plate-shaped carbon powder particles,with an amorphous carbon coating overlaid onto the powder, with theresulting carbon structure being incorporated into the negativeelectrode plate of an intercalating, secondary lithium battery. UnitedStates Patent Publication 2015/0194668 describes a composite graphiteparticle for use as an active material in a nonaqueous secondary batteryin which the particle comprises graphite and metallic particle capableof alloying with lithium.

Separately, carbons are conductive powders may be mixed with particulateactive materials to facilitate conduction of electronics in theelectrode structure during discharge. For example, in lithium-irondisulfide primary batteries, U.S. Pat. No. 8,785,044 discloses a cathodeformulation relying on a combination of graphite and acetylene black toenable significantly larger amounts of active iron disulfide in thecathode coating. Of course, the electrochemical reaction inherent tothis system results in the formation of conductive iron, so the ultimateconsiderations in the amount and dispersion of carbon in the initialcathode formulation is distinct from other battery systems which producedifferent reaction products.

As a separate example, U.S. Pat. No. 6,828,064 discloses the use ofexpanded graphite particles in electrochemical cells, particularlyalkaline cells having cathodes formed from a mixture of manganesedioxide and conductive carbon materials forming a conductive matrix.Because manganese dioxide has a relatively low level of conductivity,conductive agents such as graphite, expanded graphite and/or acetyleneblack are commonly used as conductive agents, although their use entailsvolumetric and unwanted absorption concerns.

U.S. Pat. No. 8,298,706 provides a generic listing of the range ofpotential conductive additives in alkaline batteries. Anywhere between2-35 wt. % of conductive additive can be selected from a list thatincludes graphite, carbon black, acetylene black, partially graphitizedcarbon black, carbon fibers and/or nanofibers, carbon nanotubes, andgraphene, as well as various non-carbon based conductors (e.g., silver,gold, or nickel powders). The graphite is further characterized asnon-synthetic/natural non-expanded graphite, synthetic non-expandedgraphite, non-synthetic/natural expanded graphite, synthetic expandedgraphite and oxidation-resistant, synthetic non-expanded graphite.

U.S. Pat. No. 8,920,969 also identifies a number of differentcarbon-based conductor materials that may be appropriate for use inalkaline batteries. However, it is suggested that relatively low weightpercentages (less than 3.75 wt. %, with preferred ranges between 2.0 and3.5 wt. %) of conductor enable the inclusion of higher levels of activematerial. In the same manner, it is suggested that the conductor consistonly of expanded graphite, as unexpanded graphite is significantly lessconductive and, by implication, less desirable for use in alkaline orother batteries.

United States Patent Publication Nos. 2012/005229 and 2008/0116423generally describe agglomerated cathode active material structures forsecondary (i.e., rechargeable) nonaqueous batteries. The use ofagglomerates in alkaline battery anodes has also been noted in U.S. Pat.Nos. 7,709,144 and 7,332,247.

Mixtures of active material (e.g., manganese dioxide) and conductivecarbons usually result in randomized dispersion of the materials. Whenthe conductive carbons have a particular shape (e.g., graphite), theorientation of those shapes will also occur randomly. FIG. 1 illustratesa non-optimized, random distribution of plate-shaped graphite particlesdispersed within a manganese dioxide electrode mixture, with manganesedioxide particles or agglomerates M mixed with graphite particles Ghaving essentially random orientations in comparison to the putativecurrent flowing through the mixture (as generally represented by I).

The following description and the drawings disclose various illustrativeaspects. Some improvements and novel aspects may be expresslyidentified, while others may be apparent from the description anddrawings.

SUMMARY OF INVENTION

One embodiment of the invention comprises a positive electrode for analkaline primary battery having any combination of the followingfeatures:

-   -   at least one active material;    -   a particulate conductive material dispersed within the active        material;    -   wherein the particulate conductive material has a flat planar        structure with at least 90% of the particulates aligned in        substantially identical spatial orientations;    -   wherein the electrode possesses a circular cylindrical shape;    -   wherein the particulate conductive material comprises        anisometric graphite;    -   wherein the active material comprises manganese dioxide; and    -   wherein the active material consists of at least 90 wt. % of        manganese dioxide.

Another embodiment of the invention comprises a method of making apositive electrode for an alkaline primary battery having anycombination of the following features:

-   -   providing a particulate, conductive material having a basal        plane to a cathode mixture including at least one active        material;    -   dispersing the conductive material within the cathode mixture so        that at least 90% of the particles of the active material have a        substantially parallel orientation along their basal planes;    -   wherein the orientation of the conductive material is        accomplished by at least one of: stretching, freeze casting,        co-extrusion, and magnetic orientation.

A further embodiment of the invention comprises a positive electrode foran alkaline primary battery having any combination of the followingfeatures:

-   -   at least one particulate active material;    -   a first conductive material;    -   a second conductive material having a different physical size in        comparison to the first conductive material;    -   wherein the first conductive material is entrained within        particles of the active material to form active material        agglomerates;    -   wherein the second conductive material adheres to at least a        portion of a surface of the active material agglomerates;    -   wherein the first conductive material forms a conductive pathway        within individual active material agglomerates and the second        conductive material forms a conductive network between a        plurality of active material agglomerates;    -   wherein the first conductive material comprises synthetic        graphite;    -   wherein the second conductive material comprises at least one        selected from the group consisting of: unexpanded graphite,        expanded graphite, graphene, graphite tubes, and graphite rods;    -   wherein the first conductive material consists of synthetic        graphite and the second conductive material consists of an        anisometric graphite;    -   wherein the first conductive material is oriented in common        direction within the electrode;    -   wherein particulate active material comprises manganese dioxide;    -   wherein at least 90 wt. % of the electrode consists of manganese        dioxide; and    -   wherein the electrode has a tubular cylindrical shape.

A still further embodiment of the invention comprises a method of makinga positive electrode for an alkaline primary battery having anycombination of the following features:

-   -   a first mixing step including dispersing a first conductive        material in a particulate active material and forming        agglomerates in which the first conductive material is entrained        within the agglomerates;    -   a second mixing step, performed at a lower energy in comparison        to the first mixing step, including adhering a second conductive        material with at least a portion of a surface of the        agglomerates;    -   wherein the second conductive material comprises particles of a        larger size in comparison to particles of the first conductive        material;    -   wherein the forming of agglomerates comprises compacting the        dispersed first conductive material and particulate active        material;    -   wherein the active material comprises manganese dioxide;    -   wherein the manganese dioxide consists of least 90 wt. % of the        positive electrode;    -   wherein the first conductive material comprises synthetic        graphite;    -   wherein the second conductive material comprises at least one        selected from the group consisting of: unexpanded graphite,        expanded graphite, graphene, graphite tubes, and graphite rods;    -   orienting the first conductive material to align the first        conductive material in a common direction within the electrode;    -   wherein the orienting of the first conductive material includes        at least one of:

stretching, freeze casting, co-extrusion, and magnetic orientation;

-   -   forming the cathode structure produced by the second mixing step        into a tubular cylinder; and    -   wherein the forming the cathode structure is achieved by ring        molding or impact molding.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various systems, apparatuses,devices and related methods, in which like reference characters refer tolike parts throughout, and in which:

FIG. 1 is a diagrammatic illustration of how graphite flakes dispersewithin an exemplary cathode mixture for an alkaline battery.

FIGS. 2A and 2B are diagrammatic illustrations of preferred orientationsof the graphite relative to the anticipated current flow according tocertain embodiments of the invention.

FIG. 3 diagrammatically illustrates another embodiment of the invention.

FIG. 4 is a cross-sectional view of a standard, cylindrical alkalinebattery useful to certain embodiments of the invention.

The figures of any document incorporated by reference are similarlyincorporated by reference herein.

DETAILED DESCRIPTION

Reference will now be made to exemplary embodiments, examples of whichare illustrated in the accompanying drawings. It is to be understoodthat other embodiments may be utilized and structural and functionalchanges may be made. Moreover, features of the various embodiments maybe combined or altered. As such, the following description is presentedby way of illustration only and should not limit in any way the variousalternatives and modifications that may be made to the illustratedembodiments. In this disclosure, numerous specific details provide athorough understanding of the subject disclosure. It should beunderstood that aspects of this disclosure may be practiced with otherembodiments not necessarily including all aspects described herein, etc.

As used herein, the words “example” and “exemplary” means an instance,or illustration. The words “example” or “exemplary” do not indicate akey or preferred aspect or embodiment. The word “or” is intended to beinclusive rather than exclusive, unless context suggests otherwise. Asan example, the phrase “A employs B or C,” includes any inclusivepermutation (e.g., A employs B; A employs C; or A employs both B and C).As another matter, unless context suggest otherwise, the articles “a”and “an” are generally intended to mean “one or more” and the use ofplural may be exemplary rather than mandatory.

Unless noted to the contrary, all methods and experiments contemplateambient environmental conditions, including temperature and pressure.Further, common analytical instruments and/or laboratorytechniques—including but not limited to standardized testing protocolssuch as those published by the American National Standards Institute andother, similar organizations—may be used to inform the methods,compositions and other material characteristics disclosed herein.

While it is generally known that orientation of conductive carbons insecondary cells may impart certain advantages (as noted above), artisansin the field of alkaline primary batteries had placed a greater oneffectively and completely mixing active and inactive species incathodes. The inventors realized additional advantages might be realizedin this system if the conductive carbons could be oriented in a moreordered and optimized manner relative to the anticipated current flowthrough that mixture.

In particular, as shown in FIGS. 2A and 2B, if graphite G were orientedso that current flow I occurred through the basal plane form by line B-Bwithin each graphite particle (i.e., so that current followed from edgeto edge), electronic conductivity and ionic diffusivity would beimproved, as the relative number of graphite particles required to forman electronic connection would be minimized. FIG. 2B diagrammaticallyillustrates the collective effect this preferred orientation might have,with G indicating graphite particles, M showing the particulate activematerial (e.g., manganese dioxide) and I representing the anticipatedcurrent flow.

In order to achieve such uniformity in the alignment of the graphite, anumber of processes could be employed. For example, after mixing theactive and inactive materials, the cathode could be mixed so as to havedoughy or rubbery consistency, so that it might be stretched andgenerally worked in order to urge the graphite particles into a uniformorientation consistent with the stretching/working. Freeze casting,coextrusion of active material and properly aligned conductivematerial(s), and/or magnetic alignment (either through the use ofmagnetic nanoparticles or other magnetics additives adhered to theconductive material or through the use of a conductor that issusceptible to reorientation when exposed to a magnetic field) are otherpotential processes by which the desired alignment of the conductivematerial within the positive electrode may be achieved.

Uniformity in the alignment of the graphite (or other conductivematerial) is achieved when at least 60%, more preferably at least 90%,and most preferably at least 95% of the particles are substantiallyaligned. Substantial alignment is determined by projecting an imaginaryaxial line on each particle's elongated axis, with the specifiedpercentage (e.g., 60%, 90%, or 95%) of such imaginary axial lines withina range of no more than 60 degrees, more preferably no more than 45degrees, and most preferably no more than 30 degrees of one another.

Of course, the bobbin-style construction normally employed bycylindrical alkaline batteries (described in more detail below) presentsunique challenges insofar as the current flow is most likely to be in aradial plane, owing to the circular tube structure of standard alkalinebattery cathodes. Nevertheless, stretching/working might provide usefulfor coin cells. Furthermore, so long as the graphite formed consistentpathways, advantages might be realized even without forming straight,parallel planes.

Realizing the difficulties in achieving perfect orientation of graphite,additional and/or alternative approaches may be preferred in certainsituations. For example, by employing a variety of conductive carbonsand/or by introducing the carbons at differing intervals during themixing/manufacturing process, optimized cathode structures can beachieved. In particular, active material based-mixtures (e.g., manganesedioxide and/or a combination of active materials, binders and optionalrheology aids) are processed in the presence of one type of carbon tocreate agglomerates with conductive material entrained therein. Theseagglomerates are be subsequently mixed and processed with a secondconductor so as to optimize the conductivity of the entire mix. In thisarrangement, the relative size of the differing carbons is tailored tothe processing step and point in time in which they are introduced tothe cathode mixture.

FIG. 3 illustrates one embodiment that can result from this two-carbonapproach. Agglomerates A comprise a plurality of active materialparticulates M adhered to one another with a first conductive materialG1 interposed and adhered within the agglomerate A. A separateconductive material G2 adheres to at least a portion of the exteriorsurface of each agglomerate. The O:C ratio for agglomerates A could bethe same as different from that of the entire electrode/cathodestructure. As above, the current flow (not shown in FIG. 3) is expectedto move through this material in a consistent direction, although thestructure depicted in FIG. 3 is well suited to adapt to whateverdirection that preferred flow may be.

Preferably, conductive material G1 is an expanded or unexpanded graphiteor other conductive carbon that is mixed with the active materialparticulates M in a high energy mixing method. This fluff mixture isthen densified via, as a non-limiting example, a twin roll calendar. Theresulting densified/comp acted mixture will consist mostly ofagglomerates A with conductive materials effectively entrained withinthe agglomerate.

The second conductive material G2 has different, and preferably larger,size in comparison to the first conductive material G1. More preferably,the material G2 is also larger than the active material particulates Mand the agglomerates A, as this will simplify the process of coating theagglomerates A. Ultimately, the material G2 is mixed via a low energymixing method to distribute and effectively coat the material G2 ontoand in between the agglomerates.

In forming and coating (or otherwise adhering) the above mentionedcomponents during either or both of the high and low energy mixingphases, it may be possible to use rheology or processing aids to improvethe overall process. Such aids would assist in establishing andmaintaining the desired flow of particles. In the same manner, knownsurfactants and/or adhesive binders could be incorporated in order toachieve the desired structure, as shown in FIG. 3 and described herein.Additionally or alternatively, functional groups or other aspects of theconductive carbon's surface could be selected and/or engineered toachieve these same properties. Collectively, such additives are wellknown, and may include by way of non-limiting examples materials such ascoathylene, polytetrafluoroethylene (PTFE), and/or barium sulfate-basedmaterials.

In one embodiment, material G1 is a synthetic graphite, such as KS6 orMX15, which are both sold by Imerys Graphite & Carbon of Bodio,Switzerland. Generally speaking, it is desirable for material G1 to havea relatively consistent, smaller shape (expanded or unexpanded) and sizein comparison to both material G2 and active material particulates M.

The material G2 should be a highly anisometric graphite, such as anexpanded graphite, graphene and/or graphite tubes or rods. Exemplaryforms of such conductive materials are sold under a variety of tradenames by Superior Graphite of Chicago, Ill., USA; Chuetsu Graphite WorksCo., Ltd. of Osaka, Japan; and/or Imerys as noted above.

Because a more compact carbon is integrated within the active materialagglomerate, it is not as important to align the second, moreanisometric carbon in a unitary direction. Instead, the second carbonneeds to adhere to a portion of the surface of the agglomerates so as toprovide a conductive path that follows the contours of the activematerial agglomerates. As used herein, “adhere” may include coatingprocesses (with or without the use of binders) and/or other processeswhich result in the components remaining in close proximity (e.g.,mechanical, chemical, dispersive, electrostatic, diffusive, etc.) Theresulting cathode structure is volumetrically optimized becauseinterstices within and between the agglomerates that would otherwise bevoids can now be filled with differing conductive materials without theneed to substitute conductive material for the active material itself.

Further, it will be understood that that the presence of the conductivecarbons is intended to enhance the overall conductivity of the cathodestructure itself. As such, the amount of conductors G1 and/or G2 shouldbe minimized so as to allow for the addition of cathode active materialM to maximize discharge performance. In the same manner, owing to thehydrophobicity of certain carbons and the need to retain ionicconductivity, a complete and hermetic coating of the agglomerates is notdesired. In fact, the use of carbon, and more specifically graphite,coating on the agglomerates should be sufficient to maintain aconductive network between the plurality of agglomerates in the cathode,while the carbon/graphite within the agglomerates is intended to enhanceinternal conductivity.

The invention is expected to have particular utility in the realm ofprimary alkaline battery cathodes. Such cathodes must possess certainunique characteristics, particularly in comparison to rechargeablebattery electrodes and/or systems relying on current collectors, organicsolvent electrolytes, additional conductive diluents (e.g., metalpowders, etc.), and the like. Foremost, the structure described herein,particularly with respect to agglomerates incorporating two differenttypes of graphite, should be well-suited to the formation of impact orring molded structures. Because these structures do not need to retainany cycling capabilities, the stability of the structure is of minimalconcern after repeated charge and discharge cycling. Further thereliance on a highly conductive aqueous electrolyte largely obviates theneed to extensively use discrete, intra-electrode current collectiondevices (beyond the graphites entrained in and coated partially on theagglomerates), thereby freeing up more volume that may be devoted toactive material.

Any of the foregoing processes could be used in combination with oneanother so as to achieve the desired conductor orientation and/orconductive cathode structure. The ultimate end goal is to create anengineered cathode structure that is volumetrically optimized forconductivity and/or maximum active material content. Batteriesincorporating these cathode structures, and particularly standard sizedcylindrical batteries (e.g., AA-, AAA-, C-, and D-sizes) and standardsized coin and button cell batteries (like the types used in watches,hearing aids, and small electronic devices), are also contemplated.

The efficacy of cathode structure formation according to the variousembodiments described herein may be measured indirectly, particularly tothe extent it may prove difficult to directly detect the alignment (orlack of alignment) of the conductive particles. Consequently, a controlcathode mix may be formed through conventional, random dispersion of thecathode components. In parallel, any of the inventive structures areformed from a similar mixture, but further utilizing the methodsdescribed above (e.g., stretching/working, high and low energy stagedmixing of different components, etc.).

The control and inventive electrodes thus formed are then subjected toidentical testing protocols. For example, an array of microprobes may beused to “map” the conductivity at discrete locations across the lengthand width of the electrodes. Such mapping provides insights as to theconsistency of conductivity across each electrode's face, with theinventive cathode expected to exhibit more consistent conductivity amongthe various mapped locations in comparison to the control electrode.Further, when the conductivity of the entire inventive electrode iscompared against the control cathode, the inventive cathode should showsignificant improvements in its overall conductivity owing to theorganized structure of conductive networks as described herein. In theevent it is not possible to formulate a control, comparisons could bemade to previously known and/or commercially available alkaline consumerbatteries which, as of the date of this application, do not incorporatethe inventive cathode structures. Also, resistivity and/or other similarperformance metrics correlating to the presence and alignment ofconductive materials in the electrode may be used in addition to or inplace of conductivity measurements.

Of course, traditional imaging and analytic techniques may also be usedto verify the existence of the desired orientation and/or cathodestructure. By way of non-limiting example, scanning electron microscopyand computerized tomography are potential tools.

While traditional alkaline primary cells and cathodes are anticipated toobtain the most benefits from the invention, it will be understood thatmultiple active materials may be used. For example, in addition tomanganese dioxides, active additives such as nickel oxyhyrdroxide,delithiated metal oxides and other materials could be used. Preferably,the active materials used in this invention will comprise at least 50wt. %, at least 75 wt. %, and at least 90 wt. % of manganese dioxide ormanganese oxide-based materials in comparison to the total mass of allcathode components in a dry state prior to any mixing (i.e., the finalmolded cathode, which is free from any separate substrate/currentcollector).

For the sake of completeness, FIG. 4 illustrates other components ofelectrochemical cells according to certain embodiments of the invention.Specifically, an electrochemical cell 1 is shown, including a containeror can 10 having a closed bottom end 24, a top end 22 and sidewall 26there between. The closed bottom end 24 includes a terminal cover 20including a protrusion. The can 10 has an inner wall 16. In theembodiment, a positive terminal cover 20 is welded or otherwise attachedto the bottom end 24. In one embodiment, the terminal cover 20 can beformed with plated steel for example with a protruding nub at its centerregion. Container 10 can be formed of a metal, such as steel, preferablyplated on its interior with nickel, cobalt and/or other metals oralloys, or other materials, possessing sufficient structural properties,that are compatible with the various inputs in an electrochemical cell.A label 28 can be formed about the exterior surface of container 10 andcan be formed over the peripheral edges of the positive terminal cover20 and negative terminal cover 46, so long as the negative terminalcover 46 is electrically insulated from container 10 and positiveterminal 20.

Disposed within the container 10 are a first electrode 18 and secondelectrode 12 with a separator 14 there between. First electrode 18 isdisposed within the space defined by separator 14 and closure assembly40 secured to open end 22 of container 10. Closed end 24, sidewall 26,and closure assembly 40 define a cavity in which the electrodes of thecell are housed.

Closure assembly 40 comprises a closure member 42 such as a gasket, acurrent collector 44 and conductive terminal 46 in electrical contactwith current collector 44. Closure member 42 preferably contains apressure relief vent that will allow the closure member to rupture ifthe cell's internal pressure becomes excessive. Closure member 42 can beformed from a polymeric or elastomer material, for example Nylon-6,6, aninjection-moldable polymeric blend, such as polypropylene matrixcombined with poly(phenylene oxide) or polystyrene, or another material,such as a metal, provided that the current collector 44 and conductiveterminal 46 are electrically insulated from container 10 which serves asthe current collector for the second electrode 12. In the embodimentillustrated, current collector 44 is an elongated nail or bobbin-shapedcomponent. Current collector 44 is made of metal or metal alloys, suchas copper or brass, conductively plated metallic or plastic collectorsor the like. Other suitable materials can be utilized. Current collector44 is inserted through a preferably centrally located hole in closuremember 42.

First electrode 18 is preferably a negative electrode or anode. Thenegative electrode includes a mixture of one or more active materials,an electrically conductive material, solid zinc oxide, and a surfactant.The negative electrode can optionally include other additives, forexample a binder or a gelling agent, and the like.

Zinc is the preferred main active material for the negative electrode ofthe present invention. Preferably, the volume of zinc utilized in thenegative electrode is sufficient to maintain a desiredparticle-to-particle contact and a desired anode to cathode (A:C) ratio.The volume of zinc in the negative electrode can range from about 20 toabout 32 volume percent, more preferably about 24 to about 30 volumepercent. Notably, the solids packing of the negative electrode mixremains relatively unchanged from previously known designs, despite alower overall concentration of zinc, because the relative volumecontributions by the zinc and the zinc oxide are similar. The volumepercent zinc is determined by dividing the volume of zinc by the volumeof the negative electrode just prior to dispensing the negativeelectrode into the separator lined cavity as will be explained below.The volume percent zinc must be determined before dispensing thenegative electrode into the separator basket because a portion of theelectrolyte incorporated into the negative electrode migrates into theseparator and cathode as soon as the negative electrode is inserted intothe cavity defined by the separator. The volume percent zinc is based onthe density of zinc (7.13 g/cc), the volume of the negative electrodemix and the weight of the negative electrode mix.

Zinc suitable for use in the present invention may be purchased from anumber of different commercial sources under various designations, suchas BIA 100, BIA 115. Umicore, S. A., Brussels, Belgium is an example ofa zinc supplier. Zinc alloys may be adjusted to reduce negativeelectrode gassing in cells and to maintain test service results.

The amount of zinc present in the negative electrode ranges generallyfrom about 62 to about 72 weight percent, desirably from about 64 toabout 70 weight percent, and preferably about 67 to about 69 weightpercent based on the total weight of the negative electrode (i.e., allcomponents including zinc, additives, gelling agent and electrolyte).

In order to facilitate processing the negative electrode and to enhanceits gassing performance, stability, conductivity and the like, the zincis usually suspended in a gelling agent that effectively suspends theanode material relying on the smallest possible amount of gelling agent.For example, cross-linked poly(meth)acrylic acid gelling agents havefound wide-spread use, including cross-linked polyacrylate polymers soldunder the Carbopol® 940 tradename by Lubrizol Corporation of Wickliffe,Ohio, USA (hereafter, “Carbopol”). Other materials exhibiting sufficientcross-linking, such as carboxymethyl cellulose, crosslinked acrylic acidcopolymers, starch-graft copolymers of polyacrylic acid andpolyacrylamide, and alkali hydrolyzed polyacrylonitrile, may also beused.

Another common anode additive is solid zinc oxide. A higherconcentration of solid zinc oxide tend to increase high rate service,such as DSC service, but also increase negative electrode viscosity andyield stress which can create negative electrode dispensing problems.Lower concentrations of solid zinc oxide will decrease high rate DSCservice.

One or more surfactants may also be used in the negative electrodeformulation. These surfactants may be either a nonionic or anionicsurfactant, or a combination thereof is present in the negativeelectrode. A preferred surfactant may be DISPERBYK-190 from BYK-ChemieGmbH of Wesel, Germany.

The negative electrode can be formed in a number of different ways asknown in the art. For example, the negative electrode components can bedry blended and added to the cell, with alkaline electrolyte being addedseparately or, as in a preferred embodiment, a pre-gelled negativeelectrode process is utilized.

Other components which may be optionally present within the negativeelectrode include, but are not limited to, gassing inhibitors, organicor inorganic anticorrosive agents, plating agents, binders or othersurfactants. Examples of gassing inhibitors or anticorrosive agents caninclude indium salts, such as indium hydroxide, perfluoroalkyl ammoniumsalts, alkali metal sulfides, etc. In one embodiment, dissolved zincoxide is present preferably via dissolution in the electrolyte, in orderto improve plating on the bobbin or nail current collector and to lowernegative electrode shelf gassing.

Second electrode 12, also referred to herein as the positive electrodeor cathode, preferably includes manganese dioxide as theelectrochemically active material. Manganese dioxide is present in anamount generally from about 80 to about 95 weight percent and preferablyfrom about 87 to 94 weight percent by weight based on the total weightof the positive electrode, i.e., manganese dioxide, conductive material,positive electrode electrolyte and additives such as barium sulfate.Manganese dioxide is commercially available as natural manganese dioxide(NMD), chemical manganese dioxide (CMD), or electrolytic manganesedioxide (EMD). The preferred manganese dioxide for use in a cell of thisinvention is EMD. Suppliers of these materials include Tronox Limited ofStamford, Conn., USA; Tosoh Corporation of Tokyo, Japan; and ErachemComilog, Inc. of Baltimore, Md.

The positive electrode is formed by combining and mixing desiredcomponents of the electrode followed by dispensing a quantity of themixture into the open end of the container and then using a ram to moldthe mixture into a solid tubular configuration that defines a cavitywithin the container in which the separator 14 and first electrode 18are later disposed.

Second electrode 12 has a ledge 30 and an interior surface 32 asillustrated in FIG. 4. Alternatively, the positive electrode may beformed by pre-forming a plurality of rings from the mixture comprisingmanganese dioxide and then inserting the rings into the container toform the tubular-shaped second electrode. The cell shown in FIG. 4 wouldtypically include 3 or 4 rings.

The positive electrode can include other components such as a conductivematerial, for example graphite, that when mixed with the manganesedioxide provides an electrically conductive matrix substantiallythroughout the positive electrode. Conductive material can be natural,i.e., mined, or synthetic, i.e., manufactured. In one embodiment, thecells of the present invention include a positive electrode having anactive material or oxide to carbon ratio (O:C ratio) that ranges fromabout 12 to about 25. Too high of an oxide to carbon ratio increases thecontainer to cathode resistance, which affects the overall cellresistance and can have a potential effect on high rate tests, such asthe DSC test, or higher cut-off voltages. Furthermore the graphite canbe expanded or non-expanded. Suppliers of graphite for use in alkalinebatteries are noted above. Conductive material is present generally inan amount from about 3 to about 10 weight percent based on the totalweight of the positive electrode. Too much graphite can reduce manganesedioxide input, and thus cell capacity; too little graphite can increasecontainer to cathode contact resistance and/or bulk cathode resistance.An example of an additional additive is barium sulfate (BaSO₄), which iscommercially available from Solvay Bario E. Derivati S.p.A. of Massa,Italy. The barium sulfate is present in an amount generally from about 1to about 2 weight percent based on the total weight of the positiveelectrode. Other additives can include, for example, barium acetate,titanium dioxide, binders such as coathylene, and calcium stearate.

In one embodiment, the positive electrode component, such as themanganese dioxide, conductive material, and barium sulfate are mixedtogether to form a homogeneous mixture. During the mixing process, analkaline electrolyte solution, such as from about 37% to about 40% KOHsolution, is evenly dispersed into the mixture thereby insuring auniform distribution of the solution throughout the positive electrodematerials. The mixture is then added to the container and moldedutilizing a ram. Moisture within the container and positive electrodemix before and after molding, and components of the mix are preferablyoptimized to allow quality positive electrodes to be molded. Mixmoisture optimization allows positive electrodes to be molded withminimal splash and flash due to wet mixes, as well as spalling andexcessive tool wear due to dry mixes, with optimization helping toachieve a desired high cathode weight. Moisture content in the positiveelectrode mixture can affect the overall cell electrolyte balance andhas an impact on high rate testing.

One of the parameters utilized by cell designers characterizes celldesign as the ratio of one electrode's electrochemical capacity to theopposing electrode's electrochemical capacity, such as the anode (A) tocathode (C) ratio, i.e., A:C ratio. For an LR6 type alkaline primarycell of the present invention that utilizes zinc in the negativeelectrode or anode and manganese dioxide in the positive electrode orcathode, the A:C ratio is preferably greater than 1.32:1, desirablygreater than 1.34:1, and preferably 1.36:1 for impact molded positiveelectrodes. The A:C ratio for ring molded positive electrodes can belower, such as about 1.2:1.

Separator 14 is provided in order to separate first electrode 18 fromsecond electrode 12. Separator 14 maintains a physical dielectricseparation of the positive electrode's electrochemically active materialfrom the electrochemically active material of the negative electrode andallows for transport of ions between the electrode materials. Inaddition, the separator acts as a wicking medium for the electrolyte andas a collar that prevents fragmented portions of the negative electrodefrom contacting the top of the positive electrode. Separator 14 can be alayered ion permeable, non-woven fibrous fabric. A typical separatorusually includes two or more layers of paper. Conventional separatorsare usually formed either by pre-forming the separator material into acup-shaped basket that is subsequently inserted under the cavity definedby second electrode 12 and closed end 24 and any positive electrodematerial thereon, or forming a basket during cell assembly by insertingtwo rectangular sheets of separator into the cavity with the materialangularly rotated 90 degree. relative to each other. Conventionalpre-formed separators are typically made up of a sheet of non-wovenfabric rolled into a cylindrical shape that conforms to the inside wallsof the second electrode and has a closed bottom end.

The foregoing description identifies various non-limiting embodiments ofthe invention. Modifications may occur to those skilled in the art andto those who may make and use the invention. The disclosed embodimentsare merely for illustrative purposes and not intended to limit the scopeof the invention or the subject matter set forth in the claims.

What is claimed is:
 1. A positive electrode for an alkaline primarybattery comprising: at least one particulate active material; a firstconductive material; a second conductive material having a differentphysical size in comparison to the first conductive material; whereinthe first conductive material is entrained within particles of theactive material to form active material agglomerates; and wherein thesecond conductive material adheres to at least a portion of a surface ofthe active material agglomerates.
 2. A positive electrode according to1, wherein the first conductive material forms a conductive pathwaywithin individual active material agglomerates and the second conductivematerial forms a conductive network between a plurality of activematerial agglomerates.
 3. A positive electrode according to 1, whereinthe first conductive material comprises synthetic graphite.
 4. Apositive electrode according to claim 3, wherein the second conductivematerial comprises at least one selected from the group consisting of:unexpanded graphite, expanded graphite, graphene, graphite tubes, andgraphite rods.
 5. A positive electrode according to claim 1, wherein thefirst conductive material consists of synthetic graphite and the secondconductive material consists of an anisometric graphite.
 6. A positiveelectrode according to claim 1, wherein particulate active materialcomprises manganese dioxide.
 7. A positive electrode according to claim1, wherein at least 90 wt. % of the electrode consists of manganesedioxide.
 8. A positive electrode according to claim 1, wherein theelectrode has a tubular cylindrical shape.
 9. A positive electrodeaccording to claim 1, wherein the first conductive material is orientedin common direction within the electrode.
 10. A method of making acathode structure for an alkaline battery comprising: a first mixingstep including dispersing a first conductive material in a particulateactive material and forming agglomerates in which the first conductivematerial is entrained within the agglomerates; a second mixing step,performed at a lower energy in comparison to the first mixing step,including adhering a second conductive material with at least a portionof a surface of the agglomerates; and wherein the second conductivematerial comprises particles of a larger size in comparison to particlesof the first conductive material.
 11. The method according to claim 10,wherein the forming of agglomerates comprises compacting the dispersedfirst conductive material and particulate active material.
 12. Themethod according to claim 10, wherein the active material comprisesmanganese dioxide.
 13. The method according to claim 12, wherein themanganese dioxide consists of least 90 wt. % of the positive electrode.14. The method according to claim 10, wherein the first conductivematerial comprises synthetic graphite.
 15. The method according to claim14, wherein the second conductive material comprises at least oneselected from the group consisting of: unexpanded graphite, expandedgraphite, graphene, graphite tubes, and graphite rods.
 16. The methodaccording to claim 10, further comprising orienting the first conductivematerial to align the first conductive material in a common directionwithin the electrode.
 17. The method according to claim 16, wherein theorienting of the first conductive material includes at least one of:stretching, freeze casting, co-extrusion, and magnetic orientation. 18.The method according to claim 10, further comprising forming the cathodestructure produced by the second mixing step into a tubular cylinder.19. The method according to claim 18, wherein the forming the cathodestructure is achieved by ring molding or impact molding.